This relates generally to electronic devices, and more particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user.
Liquid crystal displays contain a layer of liquid crystal material. Display pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a display pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the display pixel.
The display pixels in a liquid crystal display are controlled using gate lines and data lines. Analog data signals are supplied to data lines running along columns of display pixels while gate line signals are asserted in succession in the rows of the display. Column driver circuitry is used in driving the analog data signals onto the data lines.
If care is not taken, displays can be subjected to large in-rush currents during power up. The in-rush currents arise when numerous columns driver circuits draw start-up current at the same time. Current surges may also affect column driver circuits during power-down operations. Particularly in configurations in which column drivers are mounted on a glass display substrate, power supply traces for the column drivers may have non-negligible impedances. As a result, the power supply rails for the column driver circuits may be subjected to undesirable ground bouncing and positive power supply drooping effects that can lead to circuit failures during power state transitions.
It would therefore be desirable to be able to provide improved ways to power up display circuitry in an electronic device.